1. Field of the Invention
The present invention relates to a surface mounting type semiconductor device. In particular, the present invention relates to a light-emitting diode of the above type which may advantageously be used as a backlight for a push button of a small electric appliance such as a portable telephone.
2. Description of the Related Art
Surface mounting type semiconductor devices, such as light-emitting diodes and transistors, have been used in various fields. FIG. 18 of the accompanying drawings shows an example of conventional light-emitting diode. The conventional diode Y includes a base unit 1 which is constituted by an elongated rectangular substrate 1a, a cathode 2A and an anode 2B. The substrate 1a is made of an insulating material, while the cathode 2A and the anode 2B are made of a metal piece plated with gold for example. The cathode 2A and the anode 2B are electrically insulated from each other, and each of these terminals extends from the upper surface 10 of the substrate 1a onto the lower surface 12 via a side surface 11. The diode Y also includes an LED chip 3 mounted on the upper portion 2a of the cathode 2A. The upper surface 30 of the LED chip 3 is electrically connected to the upper portion 2b of the anode 2B by a gold wire 4. The LED chip 3 and the wire 4 are enclosed by a resin coating 5 made of an epoxy resin applied on the base unit 1.
Though conveniently used, the conventional diode Y has been found disadvantageous in the following point. Since the cathode 2A and the anode 2B are made of metal, the resin coating 5 may not be firmly fixed to these terminals. This means that the bonding strength between the resin coating 5 and the base unit 1 substantially depends on the area of the disposed upper surface portion of the substrate 1a (i.e., the upper surface portion where the cathode 2A and the anode 2B are not formed).
For meeting the recent downsize requirements, the conventional diode Y has relatively small dimensions (1.6xc3x970.8 mm or 1.0xc3x97O.5 mm in a plan view). Disadvantageously, in such a small diode, it is difficult to provide the base unit 1 with a sufficiently large surface area disposed to the exterior. Thus, in use, the resin coating 5 may rather readily be detached from the base unit 1, thereby causing damage to the LED chip 3 and the wire 4.
The present invention has been proposed under the above circumstances, and its object is to improve the bonding strength between a substrate and a protection coating in a small electronic device.
According to the present invention, there is provided a semiconductor device comprising:
an insulating substrate having obverse and reverse surfaces;
a conductive terminal supported by the substrate;
a semiconductor chip mounted on the obverse surface of the substrate and electrically connected to the terminal; and
a protection coating arranged on the substrate for enclosing the chip, the protection coating being integrally formed with an anchoring portion;
wherein the substrate is formed with an engaging portion for engagement with the anchoring portion of the coating.
With such an arrangement, the anchoring portion of the coating can be firmly fitted into the engaging portion of the substrate. Thus, the protection coating is stabilized to the substrate even if the semiconductor device has a small size.
The semiconductor device may a light-emitting diode, a laser diode, a transistor and so forth.
According to a preferred embodiment of the present invention, the engaging portion of the substrate may be a through-hole in which the anchoring portion of the coating is received.
Preferably, the terminal may be formed with a bore communicating with the through-hole of the substrate.
In the above instance, the bore of the terminal may be smaller in diameter than the through-hole of the substrate.
With such an arrangement, the diametrically smaller bore of the terminal advantageously prevents the anchoring portion of the coating from being pulled out of the through-hole of the substrate. In this manner, the protection coating is more stably fixed to the substrate. The through-hole may be constant in diameter.
According to another preferred embodiment of the present invention, the through-hole may taper upward. Accordingly, the anchoring portion of the protection coating may have the same configuration. With such an arrangement, the anchoring portion is unremovably held in the engaging portion of the substrate.
Alternatively, the through-hole of the substrate may taper downward. With such an arrangement, part of a molten resin material supplied for producing the protection coating is readily introduced into the through-hole, thereby facilitating the forming of the anchoring portion of the resin coating.
According to another preferred embodiment of the present invention, the engaging portion of the substrate may be spaced from the terminal. In other words, the engaging portion may be disposed at a position where the terminal and the engaging portion do not overlap.
With such an arrangement, there is no need to provide the terminal with a bore communicating with the engaging portion. Thus, advantageously, the surface area and the volume of the terminal are prevented from being made unduly smaller.
Preferably, the engaging portion of the substrate may be a semicircular retreated portion located at an edge of the substrate.
According to another preferred embodiment of the present invention, the protection coating may be provided with an auxiliary fixing portion engaging with the reverse surface of the substrate. The auxiliary fixing portion may be connected to the anchoring portion of the coating.
With such an arrangement, the auxiliary fixing portion working together with the anchoring portion more reliably prevents the detachment of the protection coating from the substrate.
Preferably, the auxiliary fixing portion and the anchoring portion may be integrally formed with each other.
Preferably, the terminal may include a lower portion extending on the reverse surface of the substrate, and the lower portion of the terminal may be flush with the auxiliary fixing portion of the coating.
Advantageously, the substrate may be formed with another engaging portion, and the engaging portions of the substrate may be symmetrically disposed. Accordingly, the protection coating may be provided with another anchoring portion corresponding to the additional engaging portion.
With such an arrangement, due to the symmetrical arrangement of the engaging portions and the anchoring portions, the protection coating as a whole is attached to the substrate in a well-balanced manner.
Other objects, features and advantages of the present invention will become clearer from the following detailed description given with reference to the accompanying drawings.